1. Field of the Invention
The present invention relates to a transfer vessel apparatus capable of transferring samples between vacuum systems while keeping the samples in a vacuum, and to a method of storing the samples using this apparatus.
2. Description of the Related Arts
A transfer vessel apparatus is used for transferring samples between vacuum systems in which measurements are conducted in a vacuum in order to prevent reaction of samples with oxygen and water or deposition of impurities. Examples of such vacuum systems are photoelectron spectroscopic analyzer, X-ray photoelectron spectroscopic analyzers, molecular ray vapor film forming apparatus, and tunneling microscopes and so forth.
FIG. 1 is a fragmentary sectional view of a conventional transfer vessel apparatus disclosed in Japanese Patent Application Laid-Open No. 1-90027. As shown in this figure, the transfer vessel apparatus has a transfer vessel body 1 (hereinafter referred to as "vessel body") which is a hermetic vessel that can be detachably connected to external vacuum systems (not shown) through a connecting portion 2 which is provided with a shutter and a valve, both of which are not shown. A sample stage 3 carrying the sample 4 is placed in the vessel body 1. A liquid nitrogen trap 6, which is a heat-insulated vessel accommodating a cooling medium such as liquid nitrogen 5 is connected to one side of the vessel body 1 through a connecting portion 7. A heat conductive member 8 made of copper, for example is provided on the liquid nitrogen trap 6. Cooling fins 9 for cooling the atmosphere around the sample 4 without contacting the sample are connected to the heat-conductive member 8. The cooling fins 9 are provided with a sample port 10 through which the sample 4 is moved into the vessel body 1 from a vacuum system and from the vessel body 1 into another vacuum system.
The conventional transfer vessel having the described construction is used to transfer the sample 4 held in the vessel body 1 between the vessel body 1 and the vacuum system. The cooling fins 9 connected to the heat-conductive member 8 is cooled down to a very low temperature, so that the gas around the sample 4 is attracted by the cooling fins 9 by an effect known as the cold trap phenomenon. The atmosphere in the vessel body 1 is initially held at a high vacuum of 10.sup.-5 to 10.sup.-6 Torr. As a result of the cold trap phenomenon, a further enhanced vacuum in 10.sup.-7 Torr or so of the atmosphere sample 4 is produced around the. Consequently, the sample 4 can be transferred by the vacuum transfer vessel apparatus while being kept under an extremely high vacuum between different vacuum systems regardless of the distance.
However, this transfer vessel apparatus has the problems that the vacuum in the vessel body 1 inevitably is reduced when the sample 4 is held in the vessel body for a long time or when the external power source, e.g.,electric power, for the vacuum device fails. As a result, the sample is undesirably oxidized due to contact with oxygen.